Slender structure



A ril 12, 1966 YlAN-NIAN CHEN SLENDER STRUC TURE Original Filed May 1,1961 INVENTOR. Y/AM/V/M/ GHZ'A/ United States Patent 3,245,177 SLENDERSTRUCTURE Yian-Nian Chen, Winterthur, Switzerland, assignor to SulzerFreres, S.A., Winterthur, Switzerland, a corporation of SwitzerlandOriginal application May 1, 1961, Ser. No. 106,772, now Patent No.3,174,589, dated Mar. 23, 1965. Divided and this application June 10,1964, Ser. No. 374,035 Claims priority, application Switzerland, May 6,1960, 5,170/ 60 2 Claims. (Cl. 52-1) The present application is adivision of copending application Serial No. 106,772, filed May 1, 1961,now Patent No. 3,174,589, issued on March 23, 1965.

The invention relates to slender structures subjected to repeatedbending, such as, for example, chimneys, towers, masts and the like, andrelates more particularly to novel damping means for said structures.

Chimneys and other slender structures, in addition to withstanding thestatic loading caused by wind pressure in the plane of wind movement,also have to deal with those periodic forces which are produced by eddycavitation, and are operative transversely of the Wind direction thuscausing the structure to oscillate. The oscillations produced becomecritical when the frequency of eddy cavitations reaches the naturalfrequency of the structure. In masonry chimneys and riveted metal platechimneys the internal damping is usually of sufiicient magnitude so thatthe oscillatory energy of relatively small oscillatory amplitudes isreadily absorbed. However, this is generally not the case with weldedsheet metal chimneys. These structures require special measures toensure that dangerous resonance cannot occur. The known means ofachieving this object are to alter the natural frequency of the chimneyand also to release the strain by bracing the chimney with wire ropes.The disadvantage of varying the natural frequency of the chimney is thatchimney size and design often cannot be the most suitable for theparticular purpose required and, for instance, uneconomically largethicknesses of sheet must be used just to alter the natural frequency.Where dangerous oscillations occur in existing chimneys, the methodcannot be used at all. The second methodbracing by wire ropes-isexpensive and is aesthetically unsatisfactory. Accordingly, it is animportant object of this invention to provide means to reduce theoscillations of structures of the foregoing type without incurring thedisadvantages inherent in the known expedients, said means comprising atleast one dynamic oscillation damper. Other objects will appear from thefollowing detailed description.

The invention will be described with reference to an embodimentillustrated in the drawings wherein:

FIG. 1 illustrates a chimney according to the invention incorporating anoscillation damper of this invention.

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FIG. 2 is a section through the damper shown in FIG. 1 on a somewhatenlarged scale.

Referring to FIG. 1, the chimney 1 made of steel plate carries theoscillation damper structure 2 at its top end. FIG. 2 is a sectionalview of the oscillation damper structure 2 and also includes the top endof the chimney. The chimney 1 comprises an outer generated surface 10and a lining 11 with heat insulation 12 being therebetween.

FIG. 2 illustrates an oscillation damper operating by liquid friction.An annular vessel 50 secured to the outer chimney surface 10 comprisesradial perforate metal plates 51, and the sectors bounded by the plates51 are filled with a porous loose fill, such as steel swarf. The vessel50 is about half filled with a liquid forming the damping mass. A-sliquid there is used preferably an oil having a flatviscosity-temperature pattern and a low coagulation point, such assilicone oil. The advantage of the embodiment shown in FIG. 2 is thatdamping is provided at very reduced oscillations. The liquid in thevessel 50 can be loaded with suspended particles; if required,relatively coarse and non-suspendable particles, such as sand, stones,metal scrap and so on, can be added to the liquid and can move togethertherewith as the chimney oscillates. If such a filling is used in thevessel 50, the plates 51 and the porous loose fill can be omitted.

I claim:

1. In an elongated vertical structure fixed at one end and free tooscillate at the other on being subjected to a bending stress, thecombination with the free end of said structure of oscillation dampingmeans, said damping means comprising a sealed chamber mounted on thefree end of said structure, perforate plates Within said chamber anddividing the same into a plurality of interconnected compartments, and afluid within said chamber, whereby said fluid upon the oscillation ofsaid structure moves through said perforate plates from compartment tocompartment thereby to convert at least part of the energy of saidoscillation to heat and effect the desired damping.

2. A structure in accordance with claim 1 wherein said sealed chamberalso contains a mass in each of said compartments formed of a pluralityof particles movable relative to each other.

References Cited by the Examiner UNITED STATES PATENTS 2,417,347 3/1947Brown 1881 FOREIGN PATENTS 446,532 2/ 1948 Canada.

FRANK L. ABBOTT, Primary Examiner.

RICHARD W. COOKE, JR., Examiner.

1. IN AN ELONGATED VERTICAL STRUCTURE FIXED AT ONE END AND FREE TOOSCILLATE AT THE OTHER ON BEING SUBJECTED TO A BENDING STRESS, THECOMBINATION WITH THE FREE END OF SAID STRUCTURE OF OSCILLATION DAMPINGMEANS, SAID DAMPING MEANS COMPRISING A SELECTED CHAMBER MOUNTED ON THEFREE END OF SAID STRUCTUTE, PERFORATE PLATE WITHIN SAID CHAMBER ANDDIVIDING THE SAME INTO A PLURALITY OF INTERCONNECTED COMPARTMENTS, AND AFLUID WITHIN SAID CHAMBER, WHEREBY SAID FLUID UPON THE OSCIALLATION OFSAID STRUCTURE MOVES THROUGH SAID PERFORATE PLATES FROM COMPARTMENT TOCOMPARTMENT THEREBY TO CONVERT AT LEAST PART OF THE ENERGY OF SAIDOSCILLATION TO HEAT AND EFFECT THE DESIRED DAMPING.